A magnetic detecting device is known in the art. The magnetic detecting device has a magnetic-field generating means and a magnetic sensor. The magnetic sensor detects intensity of magnetic field generated by the magnetic-field generating means, which is movably provided relative to the magnetic sensor. The magnetic sensor detects a relative displacement of a detection subject, which is connected to either the magnetic-field generating means or the magnetic sensor.
This kind of magnetic detecting device is applied to, for example, a torque sensor. A magnetic sensor of the torque sensor is provided between a pair of magnetic-flux collecting members so as to detect a change of intensity of the magnetic field in accordance with rotation of a rotational shaft. The torque sensor thereby detects a shaft torque.
Another magnetic detecting device is also known in the art, according to which the detecting device has multiple magnetic sensors. When one of the magnetic sensors becomes out of order, a detection signal from another one of the magnetic sensors, which works in a normal condition, is used. For example, as disclosed in Japanese Patent Publication No. 2008-232728, a torque sensor has three magnetic sensors for transmitting each of outputs from those magnetic sensors to an electronic control unit (the ECU). The ECU compares the outputs from those three magnetic sensors and decides the outputs as normal values based on a majority decision, when two of the three outputs from the magnetic sensors coincide with each other.
In the above torque sensor, a circuit size is increased because of three magnetic sensors.
Generally, one magnetic sensor has one IC package, to which a wire harness having a power-supply line, a ground line and a signal line is connected. Therefore, in the above torque sensor, three wire harnesses are provided between the torque sensor and the ECU, when the torque sensor is of an analogue-type. As a result, space and weight for the wire harnesses are increased, when compared with a case in which the torque sensor has only one or two magnetic sensors.
In addition, although the torque sensor of the above prior art has an advantage that it is possible to determine whether the magnetic sensor becomes out of order, it is a problem that calculation load of the ECU for carrying out a process of determining the faulty magnetic sensor is increased.